A three-dimensional photofabrication method is known in which a step of selectively applying light to a photocurable resin composition to form a cured resin layer is repeated to form a three-dimensional fabricated product in which the cured resin layers are integrally stacked (See Patent Documents JP-A-60-247515, JP-A-62-35966, JP-A-62-101408, and JP-A-5-24119). The process of making the three dimensional object using the photocurable resin composition is referred to as stereolithography and the photocurable resin compositions are referred as stereolithography resin compositions.
A typical example of the photofabrication method is as follows:
light from an ultraviolet laser or the like is selectively applied to the liquid surface of a photocurable liquid resin composition, placed in a container to form a cured resin layer having a specific pattern. The photocurable resin composition for one layer is supplied over the cured resin layer, and light is selectively applied to the liquid surface of the composition to form another cured resin layer integrally stacked over the cured resin layer formed in advance. The above step is repeated a specific number of times using the same or different irradiation pattern to obtain a three-dimensional fabricated product in which cured resin layers are integrally stacked.
This three-dimensional photofabrication method has an advantage in that a three-dimensional fabricated product can be easily formed in a short time, even if the shape of the desired three-dimensional fabricated product is complicated. Therefore, the three-dimensional photofabrication method is extremely useful for trial manufacture when developing new products such as automobiles and consumer electronics, and is becoming an indispensable means for reducing the development period and cost.
Known photocurable resin compositions used for the three-dimensional photofabrication method, the following resin compositions (a) to (c) have been previously described as follows.    (a) A resin composition containing a radically polymerizable organic compound such as urethane (meth)acrylate, oligoester (meth)acrylate, epoxy (meth)acrylate, thiol-ene compounds, and photosensitive polyimide (See Patent Documents JP-A-1-204915, JP-A-2-208305, JP-A-3-160013)    (b) A resin composition containing a cationically polymerizable compound such as an epoxy compound, a cyclic ether compound, a cyclic lactone compound, a cyclic acetal compound, a cyclic thioether compound, a spiroorthoester compound, and a vinyl ether compound (See Patent Document JP-A-1-213304).    (c) A resin composition containing a radically polymerizable organic compound and a cationically polymerizable compound (See Patent Documents JP-A-2-28261, JP-A-2-75618, JP-A-6-228413, JP-A-11-310626, JP-A-11-228610, JP-A-11-240939)
Three-dimensional fabricated objects formed by the three-dimensional photofabrication method have been widely used as design models and shape-confirmation models such as prototypes of mechanical parts. A recent market trend tends to require three-dimensional fabricated products to have properties equivalent to those of a general-purpose resin (e.g., thermoplastic resin) used as a mounting material. This aims at reducing the development period and the cost of products by utilizing a three-dimensional fabricated product obtained using a radiation-curable resin not only for shape confirmation but also for evaluation tests conducted for a mounting material (e.g., assembling test, drop teat, heat resistance test, and durability test). In order to apply a three-dimensional fabricated product to such evaluation tests, a cured resin must have the same properties as those of the mounting materials.
In particular, when a mounting material is an engineering plastic such as an ABS resin, a three-dimensional fabricated product used as a plastic part prototype is required to be provided with accurate microprocessing conforming to the plan and exhibit excellent mechanical properties similar to or equal to those of the engineering plastic such as an ABS resin.
However, the technologies disclosed in Patent Documents JP-A-1-204915, JP-A-2-208305, JP-A-3-160013 (composition (a)) have a limitation in that it is difficult. to obtain a high fabrication accuracy due to large cure shrinkage. The technology disclosed in Patent Document JP-A-1-213304 (composition (b)) ensures a high fabrication accuracy, but tends to produce a brittle cured product with low toughness. Moreover, the curing speed is insufficient. The technologies disclosed in Patent Documents JP-A-2-28261, JP-A-2-75618, JP-A-6-228413, JP-A-11-310626, JP-A-11-228610, JP-A-11-240939) (composition (c)) have a limitation in that some mechanical properties (particularly toughness) are insufficient as compared with general-purpose resins.
Technology is known in which particles formed of an elastomer or the like are used to improve the mechanical strength of a three-dimensional fabricated product (See Patent Document JP-A-2003-192887). However, the mechanical properties (particularly toughness) of the resulting composition are still insufficient for use as a prototype of plastic parts produced using an engineering plastic such as an ABS resin. Moreover, the Young's modulus and the like of the composition decrease when adding a large amount of elastomer particles aiming at increasing toughness, whereby a fabricated product having high rigidity cannot obtained.
It would be desirable to have available a stereolithography photocurable resin composition that provided for cured three dimensional objects with mechanical properties similar to those of existing engineering plastics.